In the above-referenced copending application, there is disclosed a system for telemetering instrument information from the bottom of a borehole adjacent the drill bit to the surface while drilling the borehole. Particularly, the system utilizes a wireline to transmit the information from the point adjacent the drill bit to an intermediate point on the drill string. From the intermediate point the information is transmitted to the surface, utilizing a special drill string, each section of which is provided with a conductor which terminates in special contacts in the thread joints of each section. The special contacts mate when the drill string is made up to complete the electrical system. The system also includes a remotely-operated downhole connector which can be attached to the wireline prior to installing the wireline in the drill string. The connector is designed so that as the wireline is lowered into the drill string, it makes contact with its companion connector in the instrument package adjacent the drill bit. After contact is made, tension can be applied to the wireline to lock the connector to its companion connector in the instrument package. When it is desired to remove the wireline from the drill string, the tension is removed and the downhole connector operates so that it is released from its companion connector and the wireline removed. The downhole connector includes provisions to control its operation so that the connector can be repeatedly locked and released from its companion connector by applying and releasing tension on the wireline.
While the downhole connector in the copending application has proven satisfactory, at times it fails to release when desired. Its failure to release usually occurs after the system has been rotated in the borehole for several hours. Failure of the connector to release means that the tension or pull on the wireline must be increased until the terminal socket on the wireline adjacent the connector fails or the wireline breaks. This is, of course, undesirable since it means that the wireline socket must be reinstalled on the wireline and the wireline will be reduced in overall length. In addition, there is a possibility that the sudden release of the tension on the wireline will cause the wireline to rebound in the drill string and possibly, tangle itself to the extent that it will necessitate the physical removal of the wireline. This can be a costly operation since it may be necessary to cut the wireline as each individual section of the drill string is removed and physically remove the wireline. Further if the drill string is stuck in the borehole, and the wireline breaks and tangles in the drill string, it will be impossible to clear the drill string so that tools may be lowered through the drill string.